There exist currently two types of spinal connections: on the one hand osteosynthesis connections and on the other hand dynamic connections.
Spinal osteosynthesis connections are well known connections. They are frequently used to consolidate several consecutive vertebrae. Their purpose is to immobilize the vertebrae connected in a particular configuration and stabilize them during the bone fusion to allow fixed stabilization in the immobilized situation. Such connections consist of rigid rods.
On the other hand, dynamic connections are used to reduce stresses on the articular facets and intervertebral discs by allowing certain movements while, if necessary, realigning the vertebrae with respect to one another.
EP 0 669 109 discloses a device for stabilizing adjoining dorsal vertebrae. That device comprises a connecting element consisting of a band produced from elastic synthetic material and having a round transverse section. The band is intended to be fixed between at least two pedicular screws consisting respectively of a head provided with a transverse piercing. The band is fixed to the pedicular screws by inserting, through the transverse piercing, the band, which is then fixed to each of the pedicular screws by means of a clamping screw disposed along the axis of the corresponding screw, that is to say transversely to the piercing. The device also comprises a support element mounted around the band to form a body resisting pressure.
Such a connecting element does, however, have the drawback of not effecting any torsion return to oppose pivoting movements of the vertebrae around the discs.
Another important drawback of that connecting element is that it cannot be curved so as to adapt to the natural lordosis of the lumbar vertebral column.
In addition, another drawback is that the connecting element occupies a large volume (around 12.5 mm). In some circumstances, it may prove to be difficult to prevent the connecting element in question from coming into contact with the bones, such a contact causing a great deal of pain.
Moreover, such a device has a particularly important drawback relating to the need to choose the length of the support element before fitting the band. It may happen however that the effective distance between the screws after tensioning the band is not exactly that desired. However, the device as configured allows no freedom of relaxation and/or compression between the screws after the fitting of the band and support element. The surgeon therefore has no other choice than to remove the assembly consisting of support element and band in order to introduce a new support element having a different length.
WO 02/07621 discloses a connecting piece intended to maintain the spacing between at least two anchoring elements screwed into vertebrae, the connecting piece comprising: i) a flexible part divided into two continuous branches spaced apart from each other, the branches being substantially symmetrical with respect to the longitudinal axis of the piece, the ends of the branches being connected together in pairs and defining a first mean plane, and ii) two rigid parts forming rods, having a first fixing portion and a second portion, each second portion of the two rigid parts respectively extending in opposite directions from the ends of the branches connected together in pairs, the cross-section of each of the branches being less than the cross-section of the rigid parts so that the connecting piece, whose fixing portions are fixed respectively to each of the two anchoring elements, is able to bend elastically perpendicular to the mean plane during relative movement of the vertebrae, by means of which the vertebrae, kept spaced apart from one another, are able to move with respect to one another.
That connecting piece does, however, have the drawback of being able to bend only in one clearly determined direction, namely perpendicular to the mean plane formed by the two branches. The result is a mounting of the whole of the stabilization system comprising such connecting pieces requiring a certain amount of precision and therefore possibly proving tedious. Another drawback of such a connecting piece is its volume.